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Description: Severe decline and mortality of hickory (Carya spp.) occur periodically in the eastern United States. Recently, rapidly declining crowns followed by tree mortality were found to be the predominant symptoms based on a 2 year survey in six north central and northeastern states. Stems of actively declining bitternut hickory (Carya cordiformis) exhibited numerous cankers and evidence of hickory bark beetle (Scolytus quadrispinosus) (Hbb) colonization. Main stems of three affected trees (40 to 80 percent crown decline) had 178 to 1,448 bark beetle attacks. Ceratocystis smalleyi-caused cankers and xylem lesions were associated with 13 to 37 percent of these attacks. The fungus was commonly isolated from adult Hbb attacking bitternut hickory in late summer, but not from Hbb emerged from declining trees in early summer. Fifty C. smalleyi inoculations (2 to 4 m stem height) of eight bitternut hickory (13 to 28 cm diameter at breast height [d.b.h.]) resulted in reduced sap flow rates (35 to 86 percent) 12 to 14 months after treatment compared to nine controls. More xylem vessels were occluded by tyloses in inoculated trees compared to controls. These results suggest that multiple cankers and xylem dysfunction caused by C. smalleyi are likely major contributors to crown decline. The disease is apparently a result of the synergistic interaction of Hbb and the pathogen.

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